Cryogenic power source for starting jet engines

ABSTRACT

A method and apparatus for starting a gas turbine engine by vaporizing a cryogenic liquid such as liquid nitrogen, raising the resulting gas to a high temperature and pressure and applying the hot pressurized gas to the air-driven turbine starter of the gas turbine engine.

United States Patent [72] Inventor Joseph A. Council Harbor City, Calif. [21] Appl. No. 810,744 [22] Filed May 26, 1969 [45] Patented July 13, 1971 [73] Assignee Systems Capital Corporation [54] CRYOGENIC POWER SOURCE FOR STARTING JET ENGINES 16 Claims, 13 Drawing Figs.

[52] US. Cl 60/36, 152/52, 123/179 [51] Int. Cl ..F0lk 25/00, F17c 9/02, F02n 17/00 [50] Field ofSearch 60/39,51, 36; 62/53, 52; 123/179 E, 179 F [56] References Cited UNITED STATES PATENTS 2,028,119 1/1936 Boshkoff 62/53 2,0376,73 4/1936 Zenner 62/53 Primary ExaminerMartin P. Schwardon Assistant Examiner-Robert R. Bunevich Attorney-Fowler, Knobbe & Martens ABSTRACT: A method and apparatus for starting a gas turbine engine by vaporizing a cryogenic liquid such as liquid nitrogen, raising the resulting gas to a high temperature and pressure and applying the hot pressurized gas to the air-driven turbine starter of the gas turbine engine.v

PATENTEU JUL 1 3 IBYI sum 2 OF 8 INVENTOR. JUSL PA/ 6'. (UNA/ELL i IrG. 4,

E w m 5 0 0 r m N 4 e i MM 8 PATENTEU Jun 31% SHEET 5 0F 8 INVENTOR. J05PH 6 (ON/VELL 5 m w m w m {MT 4 MW WM 0 if CRYOGENIC POWER SOURCE F OR STARTING JET ENGINES BACKGROUND OF THE INVENTION This invention relates to the field of generating pneumatic power and more particularly, for generating pneumatic power for starting gas turbine engines such as those found on jet aircraft.

DESCRIPTION OF THE PRIOR ART Pneumatic energy is required to start most of the gas turbines which power present and projected pure jet and propjet aircraft. Commercial aircraft, generally, incorporate an air turbine starter mounted on the gas turbine engine. The gas turbine engine is brought up to self-sustaining speed by highpressure, high-temperature gas directed through the air turbine starter. A pressure of approximately 35 p.s.i.g. and a flow rate of approximately 100 pounds per minute is required to start the gas turbine engines on present aircraft. Presently available units for supplying this pneumatic power are either small gas turbines or mechanically driven compressors. Both of these units are high in initial cost, difiicult to maintain and expensive to overhaul. More importantly, both types of units have a limited output capacity both as to rate of flow and gas pressure. As a result, they give marginal starts on present jet engines and would have insufficient capacity to start the larger jet engines that will be used on the next generation of jet aircraft.

SUMMARY OF THE INVENTION In accordance with a principal feature of the invention, a charge of cryogenic liquid such a liquid nitrogen is injected at a predetermined rate into a pressure chamber capable of holding hot gas under pressure. The injected cryogenic liquid is then vaporized and the temperature of the resulting gas within the chamber is raised to a predetermined level. Expansion of the cryogenic liquid due to its vaporization, and the raising of the temperature of the resulting gas produces a high pressure within the chamber, which is maintained at a safe level by suitable devices. The pressurized gas is delivered from the chamber, usually through a pressure hose to an air turbine starter coupled to a gas turbine engine in an aircraft.

Unlike currently available pneumatic power sources, the power source of the present invention is capable of generating gas at a pressure considerably higher than that required by current aircraft and even higher than the pressures that will be required by future generations of aircraft. This higher-thanrequired pressure allows the use of a relatively small-diameter pressure delivery hose from the power source to the aircraft, since there is enough reserve, or excess pressure to compensate for the pressure drop along the hose due to its small diameter. In carrying out the invention, the pressure delivery hose is combined with a pressure regulator coupled between the hose and the duct system of the aircraft, so that, regardless of the amount of pressure drop along the delivery hose, the pressure of the gas being delivered to the aircraft is at a preselected level.

The amount of heat required to vaporize and to bring to a high temperature a sufficient charge of cryogenic liquid to start a gas turbine engine is very large, and the rate at which this heat energy must be delivered is extremely high. Therefore, in accordance with another feature of the present invention, the chamber in which the cryogenic liquid is vaporized contains a heat-retaining material and means are provided for raising the temperature of this heat-retaining material so as to store heat energy therein, prior to the injection of cryogenic liquid into the pressure chamber. More particularly, the chamber is provided with an inlet and an outlet to allow hot gas to be circulated through the heat-retaining material and means are provided for forcing hot gas into the inlet and through the heat-retaining material, thereby raising its temperature.

The source of this hot air may be a small gas turbine approximately the same size as is being used to start current jet engines. The advantage of this alternative is that a turbine which is too small to start the larger engines of the next generation of aircraft directly by use of its exhaust could be used to start such engines indirectly by storing the heat energy of its exhaust through the method of the present invention, and by releasing this stored energy in a short burst to convert the cryogenic liquid into hot gas at sufficient pressure to start the aircraft engine. 7

Alternatively, the pressure chamber inlet and outlet may be connected in a closed pneumatic loop to the heat exchange duct of a heater. In this alternative, means will be provided for force circulating a gas through the closed system, thereby conveying heat energy from the heater to the heatretaining material in the chamber.

It should be noted that, while the principal contemplated use of the present invention is in providing pneumatic power for starting the air-driven turbine starter of a gas turbine engine, the pneumatic power generated could be used for other requirements of the aircraft, and in particular, for providing an auxiliary pneumatic power source for the pneumatic systems on the aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a highly simplified, schematic representation of one type of system incorporating features of the present invention, and intended primarily for a ground-based unit.

FIG. 2 is a similarly simplified, schematic representation of another type of system incorporating features of the present invention, and intended principally for onboard installation.

FIG. 3 is a perspective view of a ground-based pneumatic power generator incorporating features of the present invention and connected through a pressure hose to the pneumatic intake of an aircraft.

FIG. 4 is a plan view of the pneumatic power generator of FIG. 3, with the cover removed.

FIG. 5 is a side view of pneumatic power generator in the direction 5-5.

FIG. 6 is a cross section along lines 6-6 in FIG. 4 showing details of a thermal regenerator incorporated in the pneumatic power generator of FIG. 3.

FIG. 7 is a cross section along lines 7-7 in FIG. 6 showing the means by which cryogenic liquid is injected into the thermal regenerator.

FIG. 8, comprised of FIGS. 8a and 8b, when joined is a detailed schematic diagram of the pneumatic power generator shown more generally in FIGS. 3-7.

FIG. 9, is a perspective view, partially cut away, of a pressure regulator suitable for use within the system of FIG. 8.

FIG. 10 is a cross section through the pressure regulator of FIG. 9, with the valve of the pressure regulator in the open position.

FIG. 11 is a schematic representation of a hookup between the pressure supply hose of the system of FIG. 8, and an aircraft duct system.

FIG. 12 is a detailed schematic diagram ofa pneumatic control circuit in the system of FIG. 8.

BRIEF DESCRIPTION OF A FIRST EXEMPLARY EMBODIMENT As shown in FIG. 1, the first preferred embodiment of the system incorporating features of the present invention, includes a cryogenic storage tank 11 for holding a supply of cryogenic liquid, a thermal regenerator 13 for storing heat used in vaporizing the cryogenic liquid, a heater 15 used to circulate hot gas through the thermal regenerator l3 and a pressure regulator 17 for assuring that the gas generated in the thermal regenerator I3 is being delivered at a preselected pressure.

The system of FIG. 1 has two basic cycles. During the first cycle, indicated by the numeral I, hot gas is circulated through the thermal regenerator 13 so as to store a large quantity of heat in the heat-retaining material contained therein. During the second basic cycle of the system, indicated by numeral II, the cryogenic liquid is injected at a predetermined rate into the thermal regenerator 13 where it is vaporized and raised in temperature and pressure by heat transfer from the heatretaining material. The resulting hot gas is delivered through the pressure regulator 17 to an intake duct of the aircraft whose engines are to be started.

The thermal regenerator 13 is basically comprised of a pressure vessel 12 holding a matrix of heat-retaining material 14. The heater is of a standard, forced air type, having a heat exchange coil 19 housed within a chamber 21 which also contains a burner 23. The burner is supplied with fuel from a fuel tank 25 through a valve 27 by means ofa fuel pump 29. Combustion air is forced through the heat exchange coil 19 by means of blower 31.

To transfer the heat energy of the hot air from the heater 15 to the heat-retaining material 14 in the thermal regenerator 13, the heat exchange coil 19 is connected in a closed pneumatic circuit with the thermal regenerator pressure vessel 12 through ports 33 and 35 in the vessel by means of a pair of ducts 37 and 39. Air or gas is circulated through the closed system thus created by means of a second blower 41. This regeneration of the heat matrix 14 continues until it is brought up to a predetermined temperature, typically 450F. When this occurs, the blowers 31 and 41, as well as the fuel pump 29, are shut off and the thermal regenerator is ready to receive cryogenic fluid from the tank 11. Cryogenic fluid is fed from the tank 11 to the pressure vessel 12 over a line 18, and through a control valve by means of a cryogenic pump 22. Mounted in the vessel 12 and connected to receive cryogenic liquid from the line 18 is an injector 23 through which the cryogenic liquid is sprayed into the matrix 14 in a predetermined pattern and at a predetermined rate. This does not occur until there is a demand for pneumatic power from the system. At that time, the valve 20 is opened and cryogenic fluid is fed by means of the pump 22 to the nozzle 24 through which the liquid is injected into the chamber 12 onto the heatretaining material 14 at a predetermined rate. At the same time, a shutoff valve 43 leadingfrom an output port 45 of the vessel 12 is opened, and the gas which is being generated in the chamber 12 due to the injection of cryogenic liquid into it is allowed to enter a supply hose lead 47 leading from the valve 43 to the pressure regulator 17. At the pressure regulator 17 the gas pressure is modulated to a preselected level and is then delivered at that pressure level to a coupling 49 which is connected at its other end (not shown) to the intake duct of the aircraft whose engine is to be started.

In a system built essentially as shown in FIG. 1, and designed to permit successive starts of aircraft engines at short intervals, the rate at which cryogenic liquid, specifically liquid nitrogen, was fed through and injected into the pressure vessel 12, vaporized, heated, and then delivered as a gas to the coupling 49 was between 100 pounds per minute and 240 pounds per minute. The duration of a pressure cycle during which cryogenic liquid was converted into a gas and delivered to the coupling 49, was approximately 30 seconds. Thus, during each such cycle between 50 and 120 pounds of liquid nitrogen was consumed.

The heat-retaining material used in the pressure vessel 12 comprised 800 pounds of %-inch diameter alumina pellets weighing 135 pounds per cubic foot. To bring up these alumina pellets to the required temperature of 450 F., the regeneration cycle was set at 15 minutes. With these times and quantities, sufficient heat was stored in the thermal regenerator 13 to vaporize and bring up to the required pressure and temperature enough cryogenic liquid to start six aircraft engines in succession.

BRIEF DESCRIPTION OF A SECOND EXEMPLARY EMBODIMENT On present generation aircraft such as the 3-727, the B-737, and the DC-9, there is an onboard auxiliary power unit commonly referred to as the APU. This unit is a small gas turbine, shown in FIG. 2 as the unit 51, which produces shaft power which is converted to electrical energy by a generator 53. The APU also produces pneumatic power by a bleed device which extracts high-pressure gas from the compressor section of the gas turbine. The electric power produced is used for auxiliary lighting and other electrical power requirements in the airplane. Pneumatic power produced by the unit is utilized to start engines on the aircraft.

The auxiliary power units used on present generation aircraft do not produce sufficient pneumatic power to start the engines on the B-747 and similar larger aircraft. Actually, pneumatic-starting requirements for these new aircraft will be approximately double the starting requirements for engines on present aircraft. In an alternative embodiment of the inven tion, the APU is used in place of the heater 15 of FIG. 1 for regenerating, i.e., bringing up to the required temperature, the heat-retaining material 14. This alternative system which would provide onboard starting capability, would be implemented in the following manner. A thermal regenerator 13 and a cryogenic tank 11, interconnected essentially as in FIG. I, would be placed on board the aircraft in close proximity to a small APU unit of the type presently used on aircraft. A diverter valve 55 would be placed in the exhaust of the APU unit and a duct 57 would be provided to take the diverted exhaust through the thermal regenerator pressure vessel 12. Valves 59 and 61 would be provided to the thermal regenerator so that it could be isolated completely from the exhaust system of the APU.

During the regeneration cycle, gas turbine exhaust would be diverted through the heat-retaining material 14 of the thermal regenerator, raising the material to a predetermined level. Upon achieving this level, the inlet and discharge valves 59 and 61 would close and the diverter valve 55 in the gas turbine exhaust would go to the open position.

It is worth noting that the aircraft for which this alternative embodiment is contemplated, will already contain a cryogenic storage tank for use in fuel scrubbing. Therefore, a separate tank would not be required for the pneumatic power-generating system of the present invention.

To make an engine start, cryogenic liquid from this storage tank would be induced into the pressure vessel containing the heat-retaining material and the resulting hot gas would be ducted through a discharge port 63 in the pressure vessel and into the starting ducts on the airplane.

The above-described system would permit one small gas turbine to be placed aboard one of the new large aircraft, with the gas turbine itself being used primarily as an electric generating unit, and its exhaust being utilized not to start the aircraft engines directly, but being used instead to store heat in the thermal regenerator 13 in the manner described. The weight saving which this would permit would be significant. A gas turbine sufficiently large to generate enough pneumatic power to start the engines on the new type of aircraft such as the B-747 would weigh approximately 1,000 pounds more than those used on current aircraft. In contrast, the weight of the thermal regenerator would be much less, due to the fact that the thermal regenerator would have to contain only enough heat-retaining material to provide for one start. Consequently, it could be much lighter than the thermal regenerator of a ground-based system such as that shown in FIG. 1.

DETAILED DESCRIPTION OF THE FIRST EXEMPLARY EMBODIMENT I. Introduction A pneumatic power-generating unit incorporating the principles of the sy em shown generally in FIG. 1 is shown in detail in FIGS. 3--8. The following description of the system will be keyed primarily to FIG. 8 which is a detailed schematic diagram of the system. The purpose of FIGS. 3-7 is to give the reader an appreciation of the physical size and relative positions of the components comprising the system of FIG. 8. These sizes and physical relationships, however, are not critical per se and simply represent a particular choice in building the exemplary system.

in the text which follows, major components of the system of FIG. 8 will first be described in greater detail than was given with reference to FIG. 1. With the major system components thus described, the various operating modes of the system will be explained and certain optional control equipment for causing the system to operate in these modes will then be described as part of that explanation.

2. Major Components of the System a. The Cryogenic Tank The cryogenic storage tank 11 is fabricated of a material suitable for use at cryogenic temperatures. Thus, where the liquid stored in the tank is liquid nitrogen, these temperatures will be approximately 320F. The tank may be of aluminum, stainless steel, or one of the 9 percent nickel steel alloys. in the exemplary unit, the tank was manufactured of stainless steel and was insulated with a thick layer of foam to minimize boiloff of the cryogenic liquid contained therein.

Provision was also made to permit filling the tank 11 against a pressure head so as to avoid the need to dump already existing cryogenic vapor in the tank each time it is filled. Initial filling of the tank is accomplished by attaching a suitable coupling to a coupling adapter 65 connected to the bottom of the tank 11 through a manual valve 67 and the line 18. When the cryogenic storage tank 11 is initially filled, it is at ambient temperature and the cryogenic liquid entering it immediately vaporizes. This vaporization is used to pull down the tank temperature to the level of the liquid. However, a passage must be provided out of the tank 11 to permit these vapors to escape. For this purpose, a vent line 69 is provided at the top of the tank and this line may be closed by a manual vent valve 71 when the passage through the vent 69 is no longer desired. Liquid level within the tank 11 is indicated by a level gauge 73 connected to points at the top and bottom of tank 11 through lines 75 and 77. The line 75 also communicates with a pressure gauge 79 for indicating the vapor pressure in the tank 11. A pair of manually operable valves 81 and 83 are connected between the level indicator 73 and respective ones of the lines 75 and 77, so as to permit the indicator to be removed. A third manual valve 85, connected across the level indicator 73, is provided to permit adjustment of its sensitivity.

To fill the tank to a desired level, the fill valve 67 and the vent valve 71 are opened and cryogenic liquid is allowed to enter the tank until a desired level is indicated by the level indicator 73, at which time the valves 67 and 71 are shut and the supply hose is removed from the coupling 65. As will be explained in greater detail subsequently, if the tank is being filled for the first time, the vent valve 71 may have to be left open until sufficient cryogenic liquid has vaporized within the tank to bring it down to the temperature of the cryogenic liquid, approximately 320F. After this has been attained, the vent valve 71 would also be closed.

In FIG. 1, a pump 21 is shown for feeding the cryogenic liquid from the tank 11 over the line 18 into the thermal regenerator 13. Although this is a possible alternative, in the system illustrated on FIG. 8 the pump 21 is dispensed with, and instead, vapor pressure is built up in the tank 11 so as to force the cryogenic liquid through the line 18. More particularly, a tank pressure buildup coil 87 is connected to the tank for receiving cryogenic liquid from it, this coil being exposed to some temperature higher than that of the cryogenic liquid so as to vaporize the liquid and being vented through the tank so as to return the resulting gas thereto, thereby pressurizing the tank. A manually operable pressure buildup valve 89 is connected between one end of the coil 87 and the tank 11 and a pneumatically operated pressure control valve 91 is con nected in the return path of the tank pressure buildup coil 87.

The manner in which the control valve 91 is opened will be explained subsequently. Suffice it to say at this point that the valve is closed only while the tank is being filled.

To cause tank pressure to build up, the pressure buildup valve 89 is opened, allowing cryogenic liquid to flow trough the coil 87. Normally, the coil will be at atmospheric temperature and the heat transfer through the thin walls of the pressure buildup coil will vaporize the cryogenic liquid, forming gas which is vented to the top of the tank 11.

In the exemplary system of FIG. 8, provision has also been made to increase greatly the rate at which cryogenic liquid is vaporized in the coil 87, so as to compensate for any drop in tank pressure which may result when liquid is being withdrawn from the tank for injection into the thermal regenerator 13. In particular, means are provided for heating a portion of the coil 87 by enclosing that portion in a heating chamber 93 and by diverting through a duct 95 a part of the hot gas which is produced by the system during the time that cryogenic liquid is injected into the thermal regenerator 13. The flow of hot gas through the duct 95 into the chamber 93 is controlled by a heater control valve 97 which opens only when the pressure within tank 11 has dropped below a predetermined limit.

b. The Thermal Regenerator The thermal regenerator 13 is the means used in the system for vaporizing cryogenic fluid drawn from tank 11 for raising the resulting gas to a predetermined temperature and for maintaining the heated gas under a predetermined pressure. Consequently, the pressure vessel 12 must be able to withstand extremes of temperature between about 320 F. and 450 F., as well as pressures to about 150 p.s.i.g. As best seen in FIG. 6, the thermal regenerator includes two flow passages. One passage, between inlet 33 and outlet 35 of the pressure vessel 12 is for allowing hot air to be drawn through the matrix so as to raise its temperature, and the other flow passage, between the nozzle 24 and the outlet port 16 is for passing the cryogenic liquid into the chamber and drawing the resulting gas out of it. The matrix of alumina pellets 14 fills the vessel 12 almost completely, and is secured between a pair of retaining screens 28 and 30 to prevent the pellets from being carried through one of the openings 33 and 35.

c. The Regenerator Heater The regenerator heater 15 for raising the temperature of the gas circulated through the matrix 14 of the thermal regenerator during the regenerating cycle may be of any type that will increase gas temperature in a closed system. The actual heater used in the exemplary embodiment was a Model l5D9l manufactured by the Janitrol Aero-Division of the Midland-Ross Co. Principally, the heater 15 includes a heat exchange coil 19 housed in a chamber 21, and a burner 23 for heating air blown past the heat exchange coil 19. In addition to the above components, the heater 15 also includes a pair of temperature switches 101 and 103. These switches sense the temperature in the chamber 21 and in the return gas duct 39 and are used for sequencing the operation of the burner in a manner to be described subsequently with reference to the regeneration cycle of the system.

d. The Pneumatic Power Network It will be apparent that the blowers 31 and 41 could be driven by electrically powered motors. It is also apparent that fuel .from the fuel tank 25 could be fed to the burner 23 of the heater 15 by means of a pump such as the pump 29 indicated in FIG. 1. However, in the particular embodiment shown in FIG. 8, an effort was made to make the system self-powered. For this reason, air-driven motors 105 and 107 were used to drive the blowers 31 and 41, respectively. Moreover, in a manner similar to that used with the cryogenic tank 11, no pump was used with the fuel tank 25, but instead the fuel tank was pressurized, thereby forcing fuel through the valve 27 and the line 101 to the burner 23. In accordance with a feature of the invention, the pneumatic power required to drive the blower motors 10S and 107, as well as the pneumatic pressure required to pressurize the fuel tank 25, is furnished in the system of HO. 8 by vaporizing cryogenic liquid drawn from the tank 11. In particular, a line 109 leads from the pressure buildup valve 89 to a pneumatic pressure coil 111, housed in an extension 113 of the main chamber 21 of the regeneration heater 15. Thus. cryogenic liquid entering the coil 111 at a point 114 is vaporized and heated so that the resulting gas leaving the coil at a point 117 is at a pressure of approximately 100 psi. g. The pressurized gas thus produced is distributed to the blower motors 105 and 107, and to the fuel tank 25, through a control valve 115 and through a pneumatic power line 120. A standard pressure gauge 119 is provided for monitoring fuel tank pressure.

In order to prevent gas under high pressure and at a high temperature from leaving the pressurized vessel and entering the heat exchange coil 19, and the blower 41, a pair of guillotine valves 121 and 123 are placed in the ducts 37 and 39, respectively. These valves, which are quite large in diameter, are pneumatically operated by a pair of pneumatic actuators, 125 and 127, respectively. Pneumatic power for operating the actuators 125 and 127 is derived from the pneumatic pressure buildup coil 111 through a pressure-regulating valve 129, a pneumatic line 130 whose pressure level is regulated by the valve 129, and through a pair of conventional solenoidoperated three-way control valves 131 and 133.

The control valves 131 and 133 and their solenoids 132 and 134 are so connected as to make the guillotine valves 121 and 123 operate in unison. In particular, each of the valve actuators 125 and 127 has a valve-closing chamber and a valveopening chamber. The valve-closing chambers of the actuators 125 and 127 are connected in parallel to the output of the control valve 131. Similarly, the valve-opening chambers of the valve actuators 125 and 127 are connected in parallel to the output of the control valve 133. Pressure from the pneumatic line 130 is applied to an input of the threeway control valve 131 so that a path is established through the control valve 131 to the actuators 125 and 127 only when the solenoid 132 of the control valve is not energized. Conversely, the same pneumatic line 130 is connected to the control valve 133 is such a manner that pressure is transmitted through the valve to the valve-opening chambers of the actuators 125 and 127 only when the solenoid 134 of the control valve 133 is energized. lts associated control valve 131 bleeds the pressure from the valve-closing chambers of the actuators 125 and 127. Pressure is bled from the valve-opening chambers of those actuators through the control valve 133 when its associated solenoid 134 is not energized.

To control the opening and closing of the guillotine valves 121 and 123 in unison, the solenoids 132 and 134 are simultaneously actuated. Thus, to open the guillotine valves 121 and 123, the solenoids 132 and 134 are both energized, causing pneumatic pressure to be applied through the valve 133, to the valve-opening chambers of the actuators 125 and 127, and pressure to be bled from their valve-closing chambers through the three-way valve 131. When it is desired to close the guillotine valves, the solenoids 132 and 134 are both deenergized, thus allowing the pressure from the valve-opening chambers of the actuators 125 and 127 to escape through the three-way control valve 133, and pressure to be supplied through the valve 131 to the valve-closing chamber of the actuators.

e. The Duct Pressure Regulator It is an additional advantage of the pneumatic powergenerating method and system disclosed herein, that a smalldiameter pressure delivery hose may be used between the system and the aircraft. As previously explained, there is enough pressure generated in the system to make a sizeable pressure drop along the hose tolerable. To assure that the pressure within the aircraft duct system remains at a proper level regardless of the pressure drop along the hose, a pressure regulator valve 17 is connected between the hose and the aircraft duct system. This valve should be operative to modulate the flow of gas from the hose 47 to the aircraft duct system in response to a pressure variation within the duct system. The valve should, with present aircraft, limit duct pressure to about 35 p.s.i.g., and with future aircraft to about 50 p.s.i.g. A

valve particularly suitable for this purpose is the subject of a copending application by Donald A. Dotson, assigned to the assignee of the present invention, and entitled, Pressure Regulator. A description of the Dotson pressure regulator, shown herein in FIGS. 9 and 1] follows.

The Dotson pressure regulator is comprised principally of a housing 313 defining a flow port 315 and having an inlet 317 threaded for connection to the source of pressurized fluid and an outlet 319 threaded for connection to a coupling which usually forms the inlet to the duct. Extending substantially along the flow port 315 and mounted axially within the housing 313, is a generally cylindrical valve assembly 320 having a body 321 with a chamber 323 therein (FIG. 2). Mounted slideably upon the valve body 321 is a valve 325 shown in the FIG, 10 in its retracted position, opening the inlet 317. Extending through the tip of the valve 325 is an orifice 327 for admitting pressurized gas into the chamber 323 when the valve 325 is closed.

A discharge path is provided from the chamber 323 to a point outside the housing 313, which is typically at atmospheric pressure, so as to prevent pressure from building up within the chamber 323. Consequently, so long as this discharge path remains open, pressure due to the flow of gas into the chamber 323 is prevented from building up, resulting in a net force exerted upon the valve 325 by the pressurized gas at the inlet 317 and tending to push the valve open. Conversely, pressure within the chamber 323 may be caused to build up by blocking the discharge path from the chamber. As will be shown in greater detail, this pressure exerts a sufficient force upon the valve to force it into the inlet 317 so as to close it. However, to speed up the closing of the valve 325 a spring 328 is compressed within the chamber 323 between the valve body 321 and the valve 325, biasing the valve toward its closed position.

Pressure regulation is obtained by making the pressure discharge path from the pressure chamber responsive to the pressure existing in the flow port 315, so that when that pressure reaches the preselected level at which the downstream duct pressure is to be maintained, the discharge path is automatically blocked and the valve 325 is pushed toward the inlet 317, closing it and preventing the pressure within the flow port from rising further.

As best seen in FIG. 10 the discharge path from the chamber 323 extends through a bore 323 leading from the chamber to a pair of narrower bores 333 and 335 which are interconnected by an annular passage 337. The bores 333 and 335 are intersected by a bore 338 in which a plunger shaft 339, whose function will be explained subsequently, is slideably mounted. The annular passage 337 is formed by the walls of the bore 338 and by a narrowed portion of the shaft 339 between the bores 333 and 335. The discharge path continues from the bore 335 through a nozzle 341 having a bore 343 extending through its body and terminating in a constricted orifice 345 at its tip. The nozzle 341 is mounted within a recess 347 in the valve body 321 and from this recess a passage 349 leads through the bracket 322 to an opening 351 in the wall of the housing 313, and through the opening 351 to atmospheric pressure outside the housing 313. To complete the flow discharge path from the chamber 323, and to provide a means for blocking the discharge path in response to pressure reaching a preselected level within the chamber 315, the recess 347 is capped by a bellows 353. Together, the recess 347 and the bellows 353 form a chamber 355 which forms a part of the discharge path from the chamber 323.

To maintain the streamlined surface of the valve assembly, the bellows 353 is enclosed by a cone-shaped tail section 359 having openings 361 therein so as to expose the bellows to flow port pressure. Thus it may be seen that the bellows 353 is in effect a deformable wall member in the flow path from the chamber 323 and exposed upon one of its sides to the pressure prevailing within the flow port 315 and on its other side to atmospheric pressure through the passage 349.

Let it be assumed initially that the pressure regulator 311, as described thus far, has been connected between the pressure hose 47 and the coupling 49 which is in turn connected to a system of ducts 358 to which pressurized gas is to be supplied at a preselected level, as shown generally in FIG. 11. Initially, before pressure is applied on the upstream end of the supply hose 47, the valve 325 would be maintained closed against the inlet 317 by means of the biasing spring 328. Moreover, the end wall 357 of the bellows 353 would be spaced from the tip of the orifice 345 due to the fact that pressure on opposite sides of the end wall would be substantially equal, i.e., at mospheric. Upon the arrival of pressurized gas at the inlet 317 gas would enter the chamber 323 through the orifice 397 and would be discharged through the discharge path of the chamber 323, including the orifice 345, out the opening 351 of the housing 313. Consequently, the pressure within the chamber 323 would be prevented from building up to the same level that exists on the opposite side of the valve 325 and the resulting net force acting upon the valve 325 would push it toward the valve body 321, thus permitting the pressurized gas to flow through flow port 315 and through the outlet 319 into the coupling and associated duct system on the downstream side of the pressure regulator 17. This condition of the pressure regulator is shown in FIG. 10 and would continue until the pressure within the flow port 315 reached a preselected level at which time the bellows 353 will have been sufficiently deflected by the difference in pressure existing on opposite sides of its end wall 357 to press the end wall against the orifice 345 so as to close it. The pressure level at which this occurs is determined by two factors: The spring constant of the bellows and the distance between its end wall 357 and the orifice 345 in the absence of pressure within the flow port 315.

Means are provided in the Dotson pressure regulator to vary the distance between the orifice 345 and the bellows end wall 357 so as to permit the changing of the pressure level within the flow port 315 at which the orifice is closed by the bellows end wall 357. Toward this end, the nozzle 341 is slideably mounted relative to the bellows end wall 357 and means are provided for sliding the nozzle either toward or away from the bellows end wall by turning a shaft 363 which extends into engagement with the nozzle 341 through the wall of the housing 313, the bracket 324, and the wall of the valve body recess 347. More specifically, the nozzle 341 slides upon a tube 364 which is press fitted into a bore 365 extending from the constricted bore 335 next to the shaft 339. The end 366 of the shaft 363 is received in a slot 368 provided near the base of the nozzle for that purpose. In order to impart a rocking movement to the nozzle 341 as the shaft 363 is turned, the end portion 366 of the shaft 363 is made eccentric by an amount which depends upon the amount of nozzle movement desired. In particular, a pressure-selecting disc 367 is carried by the shaft 363, and detents 369a and 36% are provided for each of a plurality of preset pressure levels at which the orifice 345 is to be closed. A detent plunger 371 is biased into engagement with a selected one of the detents 369a and 36% by a biasing spring 375.

Continuing with the structural details of the adjustably mounted nozzle 341, the position selector shaft 363 is held in engagement with the slot 368 by means of a retainer ring 374 located at the bottom of the recess 347 and interlocked with a slot 376 in the shaft 363. One or more shims 377 are next placed adjacent to the retaining ring 374 so as to accurately position the bellows 353 relative to the nozzle 341. The bellows 353 is held against the shims 377, and at least partly within the recess 347, by a second externally threaded retaining ring 379 screwed into engagement with a matching set of internal threads in the lip of the recess 347. After the retaining ring 379 has been screwed into place tightly against the base of the bellows 353, the tail section 359, also having a set ofinternal threads, is screwed on the protruding end of the retaining ring 379.

In a particular version of the pressure regulator 317 of FIGS. 9-11 the regulator was designed to maintain either 30 p.s.i.g. or 50 p.s.i.g. flow port pressure. This was obtained by selecting a bellows having a stiffness such that it was deflected 0.13 inches by a flow port pressure of 50 p.s.i.g. and 0.078 inches by a flow port pressure of 30 p.s.i.g. Thus the difference in deflection between the two preselected pressure levels was 0.052 inches and therefore the eccentric end 366 of the pressure selector shaft 363 was designed to move the nozzle 341 through a total distance of 0.052 inches between its respective settings associated with the 30 p.s.i.g. and 50 p.s.i.g. levels.

In a typical system the upstream pressure at which gas is supplied at the inlet 317 is p.s.i. In order for the valve 325 to close when the discharge path from the chamber 323 is blocked by the bellows 357, the pressure within the chamber must build up to a level approaching that existing on the op posite side of the valve. It must, therefore, exceed the pressure maintained in the flow port 315. Therefore, the chamber 323 and its associated discharge path leading out through the housing 313 needs to be isolated from the flow port 315. For this reason, a pressure seal is provided between the valve 325 and the valve body 321 so as to permit the pressure within the chamber 323 to build up to levels exceeding those existing in the flow port 315. More particularly, the valve 325 is provided with a sleeve extension 381 dimensioned to fit snugly but slideably over the valve body 321. To complete the pressure seal a pair of O-rings 383 and 385 are positioned on a reduced portion 387 of the valve body 321 and are maintained in position by a spacer ring 389 and a snapring 391.

In the particular version of the Dotson valve disclosed herein, an effort has been made to reduce to a minimum the resistance to gas flow within the housing 313. Toward this end both the housing 313 and the valve assembly 320 are aerodynamically designed for minimum drag. Turning to the housing 313, it is comprised ofa metal cylinder 314 and funnel portions 393 and 395 at its opposite ends for minimizing gas turbulence caused by the change in the flow path of the gas as it enters the housing 313 and again as it leaves the housing at its outlet 319. For ease of assembly the inlet funnel portion 393 is comprised of two separate sections 393a and 393b.

Section 393a is retained within the housing 313 by means of screws 393C, and section 39312 is then attached to section 393a by means of screws (not shown). Held between section 393a and 393b is a valve seat 401 made of a material suitable to withstand temperatures up to 450 F. at which gas may enter through inlet 317. Escape of pressure from the flow port 315 to points outside the housing 313 through junctions of housing cylinder 314 and the inlet funnel portion 393 is prevented by O-rings 403 and 405 respectively situated between the section 393a and the cylinder 314 and between sections 393a and 393b. Finally, a sealing ring 407 is provided at the lip of section 393b to assure a pressure seal between the pressure regulator 311 and the pressure supply line 354 (FIG. 4). The outlet funnel portion 395 is shown as machined from a single piece of metal and is held in place at the opposite end of the housing cylinder 314 by means ofscrews 407.

The streamlined shape of the valve assembly 320 is best seen in FIG. 9. Thus, in addition to giving the valve body 321 and the valve 325 thereon a torpedo or projectilelike shape, the support brackets 322 and 324 which hold the valve assembly within the housing 313 are wing shaped.

After the gas delivery system of which the valve 317 may form a part has been in operation for a length of time, and it becomes necessary to remove the valve 317 and the coupling ,349 from the duct 358 of the aircraft to which they had been attached, it is first necessary to shut the valve 325 and to bleed whatever pressure may have remained in the flow port 315 to atmosphere. If this were not done, the remaining pressure in the duct 358 and in the flow port 315 would make separation of the coupling 49 from the duct 358 difficult. For this reason means are provided within the pressure regulator 17 for blocking the discharge passage leading from the chamber 323 independently of the pressure within the flow port 315, and means are also provided for relieving the pressure within the flow port 315 concurrently with the blocking of the discharge passage. In particular, blocking of the discharge passage is achieved by the provision of the shaft 339 and its associated annular passage 337 forming part of the discharge passage from the chamber 323. The shaft 339 is slideable within the bore 338 intersecting the constricted bores 333 and 335. When the shaft 339 is at one extreme of its travel, as shown in FIG. 3, the annular passage 337 is aligned with the bores 333 and 335, so as to complete the discharge path from the chamber 323. At the other extreme of its travel, as shown in FIG. 2, the shaft 339 blocks the path between the bores 333 and 335 so as to obstruct totally the discharge passage from the chamber 323 to the opening 351. The means for relieving pressure within the flow port 315 is a vent 409 in the wall of the housing 313 and a valve 411 mounted on the shaft 339 and movable by the shaft to close the vent 409 when the shaft is at the first extreme of its travel as shown in FIG. 10. In the illustrated version of the pressure regulator, the valve 411 was made of Teflon to withstand high gas temperatures and it was held on the end of the shaft 339 between a pair of washers 413 and 415 by a snapring 417. Together, the shaft 339 and the valve 411 comprise a plunger 412, which is held in a retracted position, with the shaft 339 at the second extreme of its travel, by means ofa spring 419 seated in a recess 421 within the support bracket 327.

Referring again to FIG. 11, and by way of summary, when the hose 47, the valve 17, and the coupling 49 are connected to the duct 358 of the aircraft whose engines are to be started, the valve 325 will be closed and the vent 409 will be open. Next, gas under pressure will be fed into the hose 47, but will be prevented from entering the flow port 315 because the valve 325 cannot open until the plunger 412 is depressed, and the annulus 337 formed by its shaft 339 becomes aligned with the ports 333 and 335 in the valve body 321. Next, the plunger 412 is depressed, completing the discharge passage from the chamber 323 and allowing the chamber 323 to be depressurized and the valve 325 to open. This is the condition of the pressure regulator 311 shown in FIG. 10. Gas under pressure will then flow through the port 315 into the duct 358 to valves 423 and 425 (FIG. 11) which are interposed between the duct 358 and respective ones of engine starters 427 and 429 in the aircraft. This flow of gas will continue until the pressure within the duct 358 and within the flow port 315 reaches the pressure level preselected by the relative spacing of the nozzle 341 and the bellows end wall 357. When this pressure is reached, the bellows end wall shuts the orifice 345 in the nozzle 341, causing the valve 325 to close. The valve 411 will be held closed against the force of the plunger spring 419 by the gas pressure within the flow port 315.

For sake of accuracy it should be noted that, in normal operation, the bellows end wall 357 does not actually reach and close the nozzle 341, and the valve 325 does not actually close the inlet 317 fully. Rather, as pressure begins to approach the level at which the bellows end wall 357 would reach the orifice 345, the bellows end wall creeps gradually toward the orifice 345, thus increasingly constricting the flow path between the orifice 345 and the bellows end wall 357, and gradually increasing the pressure within the chamber 323. As the pressure within the chamber 323 increases, the valve 325 is gradually pushed closer to the inlet 317, so as to gradually reduce the flow of gas into the flow port 315.

The next step in feeding the pressurized gas to the starter 427 and 429 is usually initiated by the pilot of the aircraft by opening one of the valves 423 and 425, so as to apply pressurized gas to a desired one of the starters 427 and 429. Typically, this will continue for approximately 15 seconds, after which the valve first opened by the pilot is closed by him. When this occurs, there tends to be a rapid pressure buildup in the duct 358, and, as explained previously, it is to prevent damage to the duct as a result of this pressure buildup that the valve 325 is made to close rapidly by use of the biasing spring 328. Thus, assuming that valve 423 had been opened and then closed, the resulting pressure buildup due to the continuing inflow of pressurized gas into the now closed system will cause the bellows 357 to close the orifice 345 and the resulting rapid pressure buildup within the chamber 323, together with the force of the spring 328 causes rapid closure of the valve 325 to prevent further inflow of gas into the flow port 315. When this occurs, the pressure within the closed system between the valves 423 and 425 at one end, and the valve 325 at the other end, will remain at the preselected level and must be released through the vent 409 by withdrawing the plunger 412, as described previously.

While a small-diameter pressure hose may be used with a pneumatic pressure-generating system built in accordance with the present invention, due to its high-pressure output, it should be understood that such a hose need not necessarily be employed, and that a standard larger size pressure hose may be used instead. Moreover, while the Dotson regulator is particularly suited for its purpose, other pressure-regulating valves may be used to regulate the pressure in the duct system to which the output of the system of the present invention is to be applied.

3. Modes ofOperation and Controls a. Introduction The system of FIG. 8 has four operating cycles during each of which the system operates in a different mode. During the first operating cycle, the system is set to receive cryogenic liquid in its storage tank 11. During the second, regenerator cycle, corresponding to cycle I in FIG. 1, the system is set to circulate hot gas between the thermal regenerator and the heater 15, with the heater being operated during this cycle to provide the heat energy required to bring the heat-retaining material 14 in the thermal regenerator up to its required temperature.

During the third, standby cycle, the guillotine valves 121 and 123 in the ducts 37 and 39 between the thermal regenerator 13 and the heater 15 are closed, and the system is held in readiness, with heat energy having been stored in its thermal regenerator matrix 14, during the preceding cycle. This standby condition exists until it is desired to generate pneumatic power such as when an engine is to be started. At this time, the system is placed in its fourth operating mode, the pressurization cycle corresponding to cycle II in FIG. 1 during which cryogenic liquid is injected from the storage tank 11 into the thermal regenerator 13, vaporized therein, heated and then fed out through the supply hose 47 to the coupling 49.

Setting of the various valves and energization of certain electrical control elements are controlled by a mode selector 135 located on a control panel 136 (FIG. 3) and mechanically coupled to four three-way control valves V1, V2, V3 and V4, and to a normally open pressure switch PSW. The valves V1 through V4 receive pneumatic power through a pneumatic line 137 connected to the primary pneumatic line 117 by a pressure-regulating valve 139. The function of the valve 139 is to drop the pressure from that in line 117 to a lower level suitable for use with the valves V1 through V4. Thus, in the exemplary embodiment the pneumatic pressure in the line 117 would be p.s.i.g., whereas the level in the line 137 would be only 70 p.s.i.g.

Each of the valves V1 through V4 has two operative positions between which it alternates as the setting of the mode selector is changed. Using the valve V1 as an example, when the valve is in its Vent" position, its outlet is blocked from its inlet and from the line 137, and is vented to atmosphere. Conversely, when the valve V1 is in its Open" position, its outlet is placed in communication with its inlet and receives pneumatic power from the pneumatic line 137. The status of the valves V1 through V4 during the four operating cycles of the system may be readily determined by referring to table I in FIG. 8b.

The function of the first control valve V1 is to prevent pressurization of the cryogenic tank 11 during the fill cycle and to permit this pressurization to take place during all other cycles of the system. For this reason, the control valve V1 is operatively connected to the pressure control valve 91 through a pressure controller 141, whose function will be explained more fully in a subsequent section.

The control valve V2 serves to depressurize the thermal regenerator 13 during all cycles except the pressurization cycle and for this purpose, the outlet of the valve V2 is connected through a line 143 to a normally closed pressure release valve 145. Briefly, the inlet to the pressure release valve 145 is connected to the portion of the duct 39 between the guillotine valve 123 and the pressure vessel 12. Thus, by opening the pressure release valve 145 under the control of the control valve V2, pressure may be released from the pressure vessel 12. To prevent rupture of the pressure vessel 12, the pressure release valve is set to release pressure from the vessel 12 at I35 p.s.i.g. independently of the control valve V2.

The third control valve V3, is used to prevent flow of cryogenic fluid from the tank 11 into the pressure vessel 12 during all cycles except the pressurization cycle. This is attained by connecting the outlet of the valve V3 to a pressure controller 147 whose output, in turn, is applied to a normally closed control valve 149, connected in the line 18 between the manually operated shutoff valve 20 and the nozzle 24.

Lastly, the valve V4 serves to prevent the flow of hot pressurized gas from the pressure vessel 12 to the tank pressure coil heating chamber 93 during all operating cycles except the pressurization cycle. For this purpose the outlet of the valve V4 is connected to the normally closed control valve 97 which is in the duct 95 between the heating chamber 93 and the pressure vessel 12.

Also controlled by the mode selector 135 is the pressure switch PSW. Its function, to be explained in greater detail with reference to the regeneration cycle, is to close a circuit from a source of electrical power, shown as the battery 153, to a set of relays whose actuation is necessary to initiate and maintain the regeneration cycle of the system.

b. The Fill Cycle The system is placed into its FILL mode of operation by the initial setting of the mode selector control 135. This will cause all four of the control valves V1 through V4 to be placed in their vent positions. Consequently, valve V1 effectively prevents circulation of vapor through the pressure buildup coil 87 and the control valve V3 causes the normally closed valve 149 to shut off the portion of the line 18 between the thermal regenerator nozzle 24 and the manual tank fill control valve 67. With the valve 20 closed, the valve 67 may be opened and the filling of tank 11 may begin On the initial filling of the tank 11, the tank and its insulation and accessories will be at ambient temperature. In order to maintain the cryogenic liquid in liquid form, it will be necessary to reduce the temperature of the tank to approximately 320F. During this initial filling, or any other filling after the tank has been allowed to run dry, the first quantity of liquid injected into the tank 11 will immediately flash into vapor. For this reason, the manual tank bleed valve 71 must be left open during this initial fill period. The flashing of cryogenic liquid into vapor acts as a refrigerant and pulls down the tank as well as its insulation and accessories to the temperature of the injected liquid. As this temperature is approached, boilotf or vaporization of the cryogenic liquid decreases and the tank bleed valve 71 may be closed, with reliance being placed upon the tank pressure regulating valve 72 which is shunted across the tank bleed valve 71. A pressure disc 74, also shunted across the tank bleed valve 71, provides additional protection in the event that the tank pressure-regulating valve 72 should fail.

If the cryogenic storage tank 11 has not been allowed to run down completely, so that its temperature need not be pulled down, the filling procedure is simplified. In this event, the tank bleed valve 71 need not be opened and cryogenic liquid may be injected directly through the coupling 65 and the manual fill control valve 67 into the tank 11.

c. The Regeneration Cycle Having filled the tank 11, the next operating mode of the system involves the storage of heat in the thermal regenerator 13, in preparation for the injection of cryogenic liquid into it. The regeneration cycle is initiated by the second setting of the mode selector control 135, placing the control valves V1-V4 into the settings indicated in table] of FIG. 815. Control valves V3 and V4 remain in the vented position in which they had been during the filling cycle. The valve V1, however, is opened in the regenerating mode so as to render operative the pressure buildup coil 87 by opening the normally closed pressure control valve 91. The control valve V2 is also opened so as to apply pneumatic power over the line 143 to the vent valve 145. The purpose of this provision is to prevent pressure buildup during the regeneration cycle in the closed pneumatic circuit comprised of the pressure vessel 12, the heat exchange coil 19, and the ducts 37 and 39 connecting them.

The valve positions controlled by the control valves V1 through V4 represent only some of the preliminary settings which are made prior to the initiation of the regeneration cycle. Most of the settings are controlled by the pressure switch PSW which is closed when the mode selector is in the regeneration mode. To begin the pressurization cycle, after having properly set the mode selector 135 for regeneration, a push-to-close" starting switch 155 is depressed. This closes a circuit from the battery 153, a pressure-responsive switch 157, the starting switch 155, the coil of a relay 161, and the nor mally closed contacts 103a of a temperature-responsive switch 103 to ground. The pressure-responsive switch 157 is normally closed and is actuated by pressure in the duct 39 at the point where pressure is supposed to be bled out of the duct by the pressure release valve 145. Thus, the pressure-responsive switch 157 is a safety feature, serving to prevent starting of the regeneration cycle so long as there is pressure in the pressure vessel 12. The temperature switch 103 is used to terminate the regeneration cycle and will be discussed further subsequently.

Assuming that the pressure release valve has been opened by the control valve V2, closing of the start switch energizes the relay 161, causing its contacts 161k and 161d to close. Closure of the contacts 161d latches the relay 161 through the stop switch 159 so that the relay remains pulled in even after the start switch 155 is released. Additionally, through the closed contacts 161d of the relay 161, battery power is applied to a Regenerate" indicator light 166 located on the control panel 136 of the unit (FIG. 3). Finally, through relay contacts 161b, battery voltage is applied over a line 163 and lines 165 and 167 to the solenoids 132 and 134, respectively. As a result, in a manner described previously, pneumatic power is applied from the pneumatic line 130 through the valve 133 to the guillotine-valve-opening chambers of the actuators 125 and 127. At the same time, due to the energization of solenoid 132, pressure is bled to atmosphere from the valve-closing chambers of the actuators 125 and 127. Thus, pressurized, the actuators 125 and 127 open their respective guillotine valves 121 and 123, unblocking the ducts 37 and 39 so as to establish the required closed pneumatic circuit between the pressure vessel 12 and the heating chamber 21. When the guillotine valves 121 and 123 are thus fully opened, they actuate a pair of microswitches 169 and 171 respectively. Through their normally opened contacts 169a and 171a, which are closed when the microswitches are actuated, the microswitches 169 and 171 complete a circuit from the energized line 163 to a line 173 leading to the solenoid 175 of a solenoid-operated three-way control valve 177. The input to the valve 177 is derived from the pneumatic line 137 and the output from the valve 177 is applied to actuate the pressure control valve 115 which in turn controls the passage of pneumatic power from the main pneumatic powerline 117 to the subsidiary pneumatic line 120 which supplies pneumatic power to the fuel tank 25 and to the blower motors 105 and 107. The pressure chamber of the control valve 115 used in the particular embodiment shown in FIG. 8 was designed to operate at a lower pressure than that being maintained in the pneumatic line 137. For this reason, a pressure-regulating valve controller 179 was connected between the valve 177 and the control valve 115. A detailed understanding of the manner in which the pressure-regulating valve controller 179 operates is not necessary at this point. It will be explained subsequently with reference to FIG. 9. It is sufficient to understand that the pressure-regulating valve controller 179 operates in response to the pressure prevailing in the line 137 when the three-way control valve 177 is opened by its associated solenoid 175, and that, when the controller 179 operates, it applies a lower pressure to the chamber of valve 115 than that which is applied to the controller. Indeed, the controller 179 operates similarly to a stepdown transformer which produces a relatively low voltage across at its output winding in response to the application of a high voltage across its input winding.

Summarizing the effect of the opening of the guillotine valves 121 and 123, when the valves are fully open, their as sociated microswitches 169 and 171 close a circuit to the solenoid-operated valve 177, causing pneumatic pressure to be applied through the pressure line 120 to the fuel tank and to the blower motors 105 and 107. Thus, in response to the opening of the guillotine valves 121 and 123, air is induced into the heating chamber 21 by the blower 31 and gas is circu' lated through the now completed pneumatic circuit between the pressure vessel 12 and the heater chamber 21.

When the blower 31 has raised the air pressure within the chamber 21 to a sufficiently high level, this condition is sensed by a normally open pressure-responsive switch 181 which is connected to the chamber 21 through a pneumatic line 183. Through its contacts 18111, the switch 18] completes a circuit from the now energized line 173, and through a line 184 to the fuel ignition unit 99. At the same time, through the normally closed contacts 101a of the temperature switch 101, a circuit is also established across the solenoid 185 of a solenoidoperated valve 187 in the line 100 leading from the pressurized fuel tank 25 to the burner 23. Thus, in response to sufficient air pressure in the heater chamber 21, fuel is applied to the burner 23 and the fuel is ignited by the ignition unit 99. Thus, in essence, the heater cycle has also been initiated in response to the opening ofthe guillotine valves 121 and 123.

Closure of the pressure switch contacts 131a in response to sufficient pressure in the heating chamber 21 also establishes a closed circuit between the energized line 173 and a line 186 leading through a diode 188 to the coil ofa relay 190 which is also connected to ground. Consequently, the relay 190 is energized and pulls in its contacts. Through its contacts 190d, the relay coil becomes connected across the battery 153 through an alternative path 192 so that, when power is subsequently removed from line 186, the relay 190 will remain energized. The reason for latching the relay 190 at this time will become apparent shortly.

As a result of the foregoing events, the regeneration cycle has been placed into operation. Gas will continue to be circulated through the closed pneumatic circuit between the pressure vessel 12 and the heater 15, and hot air will continue to be blown past the heat exchange coil 19 to deliver heat energy to the heat-retaining matrix 14 until the temperature of the matrix has been raised to a predetermined level. This is sensed by the temperature switch 103 whose sensor is in the return duct 39 leading from the pressure vessel 12.

When the matrix 14 has reached the desired temperature, the regeneration cycle is automatically terminated by the temperature switch 103. This is accomplished by the normally closed contacts of the temperature switch 103a which are connected in series with the coil of the relay 161, which it will be recalled, was energized at the beginning of the regeneration cycle by pressing on the start switch 155. The deenergized relay 161 drops out its contacts. Opening of the relay contacts 161!) interrupts the circuit through the line 163, the microswitch contacts 169a and 171a, and the line 173 to the solenoid 175 of the three-way valve 177. As a result, through the pressure-regulating valve controller 179, pressure is cut 011' from the control valve 115 and the pneumatic line 120 is cut off from its source of pneumatic power. Consequently, no further pneumatic pressure is applied to the fuel tank 25 and pneumatic power is also cut off from the blower motors 105 and 107.

The deenergization of the electric line 163 by opening of the relay contacts 161d also cuts off power from the solenoids 132 and 134 which control the application of pneumatic power to the guillotine valve actuators and 127, Consequently, pneumatic power is applied to the closing chambers of the actuators 125 and 127 through the control valve 131 and pressure is bled out of the opening chambers of the actuators through the control valve 133. As a result, the guillotine valves 121 and 123 close so as to seal the duct portions leading to the inlet and outlet ports 33 and 35 of the pressure vessel 12. Closure of the guillotine valves 121 and 123 returns their associated microswitches 169 and 171 to their original positions in which their respective contacts 16% and 1711) close. These contacts complete a circuit from ground through a line 194, a Cycle Complete" indicator light 196, contacts 190d of the relay 190, line 192, switches 157 and PSW to the battery 153, causing the cycle complete indicator light 196 to glow. It was to prepare this indicator circuit to operate in response to the closure of the guillotine valves 121 and 123, that the relay 164 was energized at the time when the heater 15 was turned Summarizing, in response to the heat-retaining matrix 14 reaching a predetermined temperature, the heater 15 has been turned off, the closed pneumatic circuit between the pressure vessel 12 and the heater coil 19 has been blocked and the blowers 31 and 41, used for the regeneration of the matrix, have been turned off.

Unless there is an immediate need for pneumatic power from the system of FIG. 8, the next step is to place the system in its standby mode, in readiness for the pressurization cycle.

(.1. The Standby Mode In the standby mode, as seen in table I of FIG. 8, the control valves V1, V3 and V4 remain in the same positions which they had during the regeneration mode. The position of the control valve V2, however, is changed from Open to Vent so as to close the pressure release valve 145. Closure of pressure release valve 145 eliminates the last opening in the pressure vessel 12, so that it will retain the heat stored in it during the regeneration cycle for a substantial length of time. The pressure switch PSW is also open, since it is not desired to continue heating the matrix 14 further. The system remains in this state in the standby mode until it is called upon to produce pneumatic power.

e. The pressurization Cycle Let it be assumed that, after the pneumatic power generator of the present invention has remained in the standby mode for some time, it is called upon to supply pneumatic power to the air turbine starter of a gas turbine engine. This is the application of the system illustrated in FIG. 3. First, the pressure supply hose 47 leading from the system would be connected through a conventional coupler 49 to the intake of the pneumatic duct network 358 of the aircraft (FIG. 1 1). Preferably, a pressure regulator 17 would be connected between the supply hose 47 and the coupler 49, to maintain duct pressure at a preselected level. Next, the manual valve 43, which had been shut during all three of the preceding modes of operation of the system, would be opened and the system would be set into its pressurization mode or cycle by the mode selector 135. In this setting, the mode selector leaves the control valve V1 in its Open position and the control valve V2 in its Vent posi tion. Consequently, the pressure control valve 91 associated with the cryogenic tank pressure buildup coil 87 remains open to maintain pressure within the tank, and the pressure release valve associated with the pressure vessel 12 remains closed, this time to permit pressure to be built up in the tank. For the first time, however, the valves V3 and V4, which had until now been in their Vent positions are opened. As the valve V3 opens, it applies pressure from the pneumatic line 137 through the pressure controller 147 to open the cryogenic liquid flow control valve 149, thus causing liquid to be expelled from the tank 11 through the line 18 into the injector 24 and through the injector onto the heat-retaining matrix 14 in the pressure vessel 12. In the manner explained previously,

the injected cryogenic liquid vaporizes and the resulting gas is heated in the pressure vessel 12, causing pressure to be built up in it to a level which is controlled by the cryogenic liquid flow control valve 149, in combination with the controller 147. Specifically, the controller 147 which is a well-known commercially available pneumatic device operates to modulate the pressure which is applied from the pneumatic pressure line 137 and through the control valve V3 to the actuator of the cryogenic liquid flow valve 149. A simplified schematic illustration of the controller 147 and of the valve 149 appears in FIG. 12.

The valve 149 is comprised of a housing 187 having a chamber 189 with an outlet port 195 and an inlet port 191 terminating in a valve seat 193. The inlet port 191 is connected through the manual valve to the line 18 which leads from the cryogenic storage tank 11. The outlet port 195 of the control valve 149 is connected through another section of the line 18 to the thermal regenerator nozzle 24. Seated on the valve seat 193 is a valve 197 carried on a valve stem 199, which is mounted upon the diaphragm 201 of a valve actuator 203. The actuator 203 also includes a chamber 205 in which the diaphragm 201 is mounted and a biasing spring 207 compressed between the chamber 205 and the diaphragm 201 and pressing the valve 197 against the valve seat 193 so as to maintain the valve in a normally closed position. To open the valve, gas or air is fed into its opening chamber 209 through an inlet 211 with an escape being provided for the gas from the chamber through an outlet 213.

The valve will open under two conditions. First, if there is excessive pressure between the manual valve 20 and the control valve 149, the valve 197 will be lifted off its seat and pressure will be allowed to escape through the openings of the nozzle 24. In this way, the control valve 149 serves as a safety valve. Indeed, all of the normally closed valves in the system perform this function so as to prevent buildup of excessive pressures in the various lines of the system. The normal way to open the control valve 149 is to apply pressurized gas to its inlet 211. This pressure will counteract the force ofthe biasing spring 207 and will lift the valve 197 off its seat by an amount which is proportional to the pressure in the opening chamber 209 of the actuator 203. This pressure in turn, may be con trolled by modulating the pneumatic pressure being applied to actuate the control valve 149. This is the function of the controller 147.

As seen in FIG. 12, the controller 147 is comprised of a housing 215 having a chamber 217 therein, with an inlet port 219 leading into one side of the chamber and an outlet port 221 leading from the opposite side of the chamber in alignment with the inlet port 219. A modulating member 223 is slideably mounted within the chamber 217, dividing it into two subchambers 2170 which is between the ports 219 and 221, and a second subchamber 21711. Compressed in the subchamber 2170, so as to bias the modulating member 223 away from the ports 219 and 221, is a biasing spring 225. To counteract the force of the biasing spring 225 in response to pressure which is to be sensed and controlled, a pressuresensing inlet 227 leads into the subchamber 217b. Accordingly, as the pressure sensed at the inlet 227 increases, the force of the biasing spring 225 is gradually overcome, and the ports 219 and 221, which are normally in full communication through the subchamber 217a, are gradually obstructed, thereby reducing the flow of pneumatic power through the controller 147. In the system of FIG. 8, the inlet port 219 is connected through a line 146 to the outlet of the control valve V3, and the outlet port 221 is connected over a pneumatic line 148 to the actuator inlet 211 of the control valve 149.

The pressure to be sensed by the controller 147 is that existing in the pressure vessel 12 and, therefore, the sensing inlet 227 of the controller 147 is connected to the pressure vessel 12 over a line 229. By proper selection of the spring constant of the spring 227 in the controller 147, the controller 147 may be adjusted so that when the pressure in the vessel 12 has reached a predetermined limit, typically 100 p.s.i.g., the

modulating member 223 obstructs the ports 219 and 221 sufficiently to allow the valve 149 to close due to insufficient pressure being supplied through the line 148 into its opening chamber 209. This shuts 011 further flow of cryogenic fluid into the pressure vessel 12 until the pressure therein drops to an acceptable level. This pressure is also indicated by a pressure indicator 231 connected to the line 229.

With the pressure vessel 12 pressurized to approximately I00 p.s.i.g., the control of flow of pneumatic power from the pressure vessel 12 of the system is transferred to the cockpit of the airplane. When the pilot or the flight engineer decides to start one of the aircraft engines, he pushes a start switch. This opens one of the starter control valves 423 and 425 (FIG. 11) and permits the high-pressure, high-temperature gas in the aircraft duct system to flow through one of the air turbine starters 427 and 429. As this occurs, pressure in the aircraft duct system drops. When this drop in pressure is sensed by the pressure regulator 17, it opens to allow sufficient high-pressure, high-temperature gas to enter the duct system of the airplane from the pressure supply hose 47 to maintain the desired and preselected pressure level in the duct system, typically 35 p.s.i.g. for current aircraft and 50 p.s.i.g. for the future generation of larger aircraft. The flow of pneumatic power from the pressure vessel 12 to the duct system of the airplane continues so long as the starter control valve actuated by the pilot remains open. The pressure level in the tank 12 will tend to drop as this occurs and this drop in pressure level will be sensed by the controller 147, causing cryogenic fluid to be fed into the pressure vessel 12 to maintain the approximately 100- p.s.i.g. pressure level within the vessel.

The rate at which cryogenic fluid is injected into the pressure vessel 12 is predetermined by the rate at which gas is to be supplied from the pressure vessel 12 to the airplane. This rate will be quite high, typically between 100 pounds and 240 pounds per minute. As a result of this large rate of liquid flow from the cryogenic tank 11, the pressure in the tank tends to drop during the pressurization cycle of the system. Auxiliary tank-pressurizing means are, therefore, provided to maintain the required tank pressure during the pressurization cycle. Means for maintaining tank pressure during the pressurization cycle comprise principally the control valve V4, the pressure controller 141, the normally closed control valve 97, and the heater chamber 93, housing a portion of the tank pressure buildup coil 87. Essentially, the pressure controller 141 may be of the same type as the pressure controller 147 discussed in detail with reference to FIG. 12. Pneumatic pressure is applied to the inlet port of the controller 141 through the control valve V1, which is opened during the pressurization mode. The pneumatic pressure thus received by the controller 141 is fed by it through its outlet port to the opening chamber of the control valve 91. Finally, the sensing input of the controller 141 is connected over a line 235 to the top of the cryogenic tank 11.

To maintain a pressure of approximately 100 p.s.i.g. in the tank 11, the controller 141 and the control valve 91 are so selected that, if the pressure within the tank 11 falls below the desired I00 p.s.i.g. level, sufiicient pneumatic pressure is applied through the controller 141 to the opening chamber of the control valve 91 to open the valve and thereby to cause cryogenic fluid to be circulated in the pressure buildup coil 87 so as to return the pressure in the tank to the desired level. The valve V1 is maintained in the open position in the regeneration and standby modes, as well as in the pressurization mode of the system, so that the control valve 91 is operative to maintain the desired pressure in the tank during these operating modes of the system as well.

Due to the rapid depletion of fuel in the tank 11 during the pressurization mode, the rate at which cryogenic liquid is vaporized in the pressure buildup tank 87 may not be sufficient. Consequently, tank pressure may continue to drop even though the control valve 91 has opened. To take care of this eventuality, the control valve 97 in the line leading to the pressure buildup coil heating chamber 93 is selected to open only when the pressure within the tank 11 drops by a predetermined amount below that at which the control valve 91 opens. To achieve this operation, the outlet port of the controller 141 is connected not only to control valve 91, but is also connected through the control valve V4, which is opened during the pressurization mode, to the opening chamber of the control valve 97. This control valve is of the same type of the control valve 91, but it is selected to open at a higher pressure than the control valve 91 by making the outlet from its opening chamber larger than the corresponding outlet of the valve 91. Consequently, if the pressure within the tank 11 drops sufficiently below the point at which the valve 91 opened, the modulating member of the controller 141 will be moved by a sufficient additional amount to cause the valve 97 to open and to allow some of the hot pressurized gas from the pressure vessel 12 to flow through the line 95 into the heating chamber 93. This will cause rapid vaporization of the cryogenic liquid in the pressure buildup coil 87 and a correspondingly rapid pressure buildup in the tank 11.

When the aircraft engine has reached the speed at which its starter 427 (or 429) is cut off, the corresponding starter control valve 423 (or 425) in the duct system 58 of the aircraft is automatically closed. As this flow through the aircraft duct system is stopped, pressure within the ducting system 58 tends to build up. This increased pressure is sensed by the pressure regulator 17 and it acts to shut off further flow of gas into the ducting system of the aircraft to prevent the desired duct pressure level from being exceeded. When the aircraft-starting operation has been completed, the coupling 49 is removed from the inlet nipple on the aircraft, and the power-generating system of FIG. 8 is returned to the standby mode.

Due to the large amount of heat stored in the thermal regenerator I3, and in accordance with an important feature of the invention, several pressurization cycles may be carried out before it becomes necessary to put the system through its regeneration cycle.

What 1 claim is:

1. A pressurized gas generator for providing pneumatic power to start a gas turbine engine comprising in combination:

a. means for storing a supply of cryogenic liquid;

b. a chamber for holding hot gas under pressure;

c. means for delivering a charge of cryogenic liquid from said means for storing to said chamber;

. a matrix of heat-retaining material within said chamber;

and

. means for raising the temperature of said heat-retaining material to a predetermined temperature, said heatretaining material being of sufficient quantity to store enough heat at said predetermined temperature to vaporize and raise the temperature and pressure of said charge ofcryogenic liquid to a predetermined level.

2. The method of generating pneumatic power for driving the air turbine starter of a gas turbine engine comprising the steps of:

a. maintaining cryogenic liquid under pressure;

b. vaporizing a portion of said cryogenic liquid and raising the temperature of the resulting gas to a predetermined level;

c. delivering said gas to said starter; and,

d. maintaining the pressure of said gas at said starter at a preselected level.

3. The method of generating pneumatic power for starting a gas turbine engine comprising the steps of:

a. storing a supply of cryogenic liquid in a first tank;

b. maintaining a heat-retaining material in a second tank;

c. raising the temperature of said heat-retaining material;

d. injecting said cryogenic liquid into thermal contact with said heat-retaining material so as to vaporize said injected cryogenic liquid; and,

e. delivering the resulting gas to said engine.

4. Apparatus for delivering pressurized gas to the intake of an aircraft pneumatic system comprising in combination:

a. a chamber for holding hot gas under pressure;

b. means for injecting cryogenic liquid into said chamber;

c. means for vaporizing said injected liquid and for heating the resulting gas to a predetermined temperature; and,

d. means for delivering said heated gas to said intake.

5. Apparatus for delivering pressurized gas to the intake duct of the air turbine starter of a gas-driven turbine comprising in combination:

a. a tank for holding cryogenic liquid;

b. a chamber for holding hot gas under pressure;

c. means for injecting said liquid into said chamber;

d. means for vaporizing said injected liquid within said chamber and,

e. means for feeding said resulting gas to said intake duct.

6. Apparatus according to claim 5 and further characterized in that said means for feeding includes a tank pressure buildup coil connected to said tank for receiving cryogenic liquid therefrom, said pressure buildup coil being exposed to a temperature higher than that of said cryogenic liquid so as to vaporize said cryogenic liquid and being vented to said tank to return the resulting gas thereto so as to pressurize said tank.

7. Apparatus according to claim 5 and further characterized in that said means for vaporizing includes:

a. a bed of heat-retaining pellets within said chamber; and

b. means for circulating hot air through said pellets so as to store in them sufficient heat to vaporize and heat several ofsaid charges ofcryogenic liquid in succession.

8. Apparatus for generating pressurized gas comprising in combination:

a. a tank for holding cryogenic liquid;

b. means for vaporizing a portion of said cryogenic liquid and for returning the resulting gas back into said tank to maintain a predetermined pressure therein;

. a chamber for maintaining hot gas under pressure and containing a heat'storing matrix, said chamber having an inlet and an outlet to allow hot gas to be forced through said matrix;

d. a heating chamber containing a heating coil through which gas to be heated may be driven; ducts connecting said heating coil across said chamber inlet and outlet to establish a closed pneumatic circuit, said ducts including at least one valve for blocking said circuit;

means for driving hot air over said heating coil;

means for circulating gas through said closed pneumatic circuit to transfer the heat energy of said hot air to said matrix;

h. means for injecting said cryogenic liquid into said chamber to vaporize said cryogenic liquid and raise its temperature by heat transfer from said matrix;

. means for delivering the resulting gas from said chamber;

and,

j. means for maintaining said valve closed during the injection of said cryogenic liquid.

9. Apparatus according to claim 8 and further characterized in that the means for maintaining said valve closed, the means for driving hot air over said heating coil, and the means for circulating gas through said closed pneumatic circuit are pneumatically powered.

10. Apparatus according to claim 1 and further characterized in that said chamber is provided with an inlet and an outlet to allow hot gas to be forced through said heat-retainine material and in that said means for raising the temperature of said heat-retaining material is a source of hot forced air to said inlet.

11. Apparatus according to claim 10 and further characterized in that said source of hot forced air is a gas turbine.

12. Apparatus according to claim 1 and further characterized in that said source of hot forced air includes:

a. a heating chamber having a heat exchange duct therein;

b. ducts connecting said heat exchange duct across said chamber inlet and outlet to establish a closed pneumatic circuit through said chamber;

0. means for driving hot air through said heating chamber over said heat exchange duct; and,

d. means for circulating gas through said closed pneumatic circuit while said hot air is being driven through said heating chamber so as to heat said heat-retaining material.

13. Apparatus for delivering pressurized gas to the intake duct of the air turbine starter of a gas-driven turbine comprising in combination:

a. a tank for holding cryogenic liquid;

b a pressure vessel for holding hot gas under pressure and having an inlet for receiving cryogenic liquid from said tank and an outlet for discharging hot gas under pressure to said intake duct;

c. means for feeding cryogenic liquid from said tank into said pressure vessel;

d. means for vaporizing the cryogenic liquid in said pressure vessel and for raising the resulting gas to a predetermined temperature and pressure; and

e. means for opening said outlet while said resulting gas is at said predetermined temperature and pressure.

14. Apparatus in accordance with claim 13 and further characterized in that:

a. said pressure vessel additionally includes a second inlet and a second outlet; and,

b said means for vaporizing includes:

1. a matrix of heat-retaining material in said pressure vessel between said second inlet and second outlet;

2. means for opening said second inlet and second outlet prior to the feeding of cryogenic liquid into said vessel;

3. means for forcing hot gas in said second inlet and out said second outlet while they are open to store heat energy in the said matrix; and,

4. means for closing said second inlet and second outlet prior to and during the feeding of cryogenic liquid into said vessel.

15. Apparatus in accordance with claim 14 and further characterized by:

a. means operable only in the absence of pressure within said pressure vessel for actuating said second inlet and second outlet opening means;

b. means for actuating said hot-gas-forcing means in response to the actuation of said second inlet and second outlet opening means;

c. means for actuating said second inlet and second outlet closing means in response to said matrix of heat-retaining material reaching a predetermined temperature; and,

d. means for deactivating said hot-gas-forcing means in response to said matrix of heat-retaining material reaching said predetermined temperature.

16. Apparatus in accordance with claim 13 and further characterized by means for increasing the rate of flow of cryogenic liquid into said pressure vessel in response to a drop in the pressure in said pressure vessel below a predetermined level so as to counteract said drop in pressure. 

1. A pressurized gas generator for providing pneumatic power to start a gas turbine engine comprising in combination: a. means for storing a supply of cryogenic liquid; b. a chamber for holding hot gas under pressure; c. means for delivering a charge of cryogenic liquid from said means for storing to said chamber; d. a matrix of heat-retaining material within said chamber; and e. means for raising the temperature of said heat-retaining material to a predetermined temperature, said heat-retaining material being of sufficient quantity to store enough heat at said predetermined temperature to vaporize and raise the temperature and pressure of said charge of cryogenic liquid to a predetermined level.
 2. The method of generating pneumatic power for driving the air turbine starter of a gas turbine engine comprising the steps of: a. maintaining cryogenic liquid under pressure; b. vaporizing a portion of said cryogenic liquid and raising the temperature of the resulting gas to a predetermined level; c. delivering said gas to said starter; and, d. maintaining the pressure of said gas at said starter at a preselected level.
 2. means for opening said second inlet and second outlet prior to the feeding of cryogenic liquid into said vessel;
 3. means for forcing hot gas in said second inlet and out said second outlet while they are open to store heat energy in the said matrix; and,
 3. The method of generating pneumatic power for starting a gas turbine engine comprising the steps of: a. storing a supply of cryogenic liquid in a first tank; b. maintaining a heat-retaining material in a second tank; c. raising the temperature of said heat-retaining material; d. injecting said cryogenic liquid into thermal contact with said heat-retaining material so as to vaporize said injected cryogenic liquid; and, e. delivering the resulting gas to said engine.
 4. Apparatus for delivering pressurized gas to the intake of an aircraft pneumatic system comprising in combination: a. a chamber for holding hot gas under pressure; b. means for injecting cryogenic liquid into said chamber; c. means for vaporizing said injected liquid and for heating the resulting gas to a predetermined temperature; and, d. means for delivering said heated gas to said intake.
 4. means for closing said second inlet and second outlet prior to and during the feeding of cryogenic liquid into said vessel.
 5. Apparatus for delivering pressurized gas to the intake duct of the air turbine starter of a gas-driven turbine comprising in combination: a. a tank for holding cryogenic liquid; b. a chamber for holding hot gas under pressure; c. means for injecting said liquid into said chamber; d. means for vaporizing said injected liquid within said chamber and, e. means for feeding said resulting gas to said intake duct.
 6. Apparatus according to claim 5 and further characterized in that said means for feeding includes a tank pressure buildup coil connected to said tank for receiving cryogenic liquid therefrom, said pressure buildup coil being exposed to a temperature higher than that of said cryogenic liquid so as to vaporize said cryogenic liquid and being vented to said tank to return the resulting gas thereto so as to pressurize said tank.
 7. Apparatus according to claim 5 and further characterized in that said means for vaporizing includes: a. a bed of heat-retaining pellets within said chamber; and b. means for circulating hot air through said pellets so as to store in them sufficient heat to vaporize and heat several of said charges of cryogenic liquid in succession.
 8. Apparatus for generating pressurized gas comprising in combination: a. a tank for holding cryogenic liquid; b. means for vaporizing a portion of said cryogenic liquid and for returning the resulting gaS back into said tank to maintain a predetermined pressure therein; c. a chamber for maintaining hot gas under pressure and containing a heat-storing matrix, said chamber having an inlet and an outlet to allow hot gas to be forced through said matrix; d. a heating chamber containing a heating coil through which gas to be heated may be driven; e. ducts connecting said heating coil across said chamber inlet and outlet to establish a closed pneumatic circuit, said ducts including at least one valve for blocking said circuit; f. means for driving hot air over said heating coil; g. means for circulating gas through said closed pneumatic circuit to transfer the heat energy of said hot air to said matrix; h. means for injecting said cryogenic liquid into said chamber to vaporize said cryogenic liquid and raise its temperature by heat transfer from said matrix; i. means for delivering the resulting gas from said chamber; and, j. means for maintaining said valve closed during the injection of said cryogenic liquid.
 9. Apparatus according to claim 8 and further characterized in that the means for maintaining said valve closed, the means for driving hot air over said heating coil, and the means for circulating gas through said closed pneumatic circuit are pneumatically powered.
 10. Apparatus according to claim 1 and further characterized in that said chamber is provided with an inlet and an outlet to allow hot gas to be forced through said heat-retainine material and in that said means for raising the temperature of said heat-retaining material is a source of hot forced air to said inlet.
 11. Apparatus according to claim 10 and further characterized in that said source of hot forced air is a gas turbine.
 12. Apparatus according to claim 1 and further characterized in that said source of hot forced air includes: a. a heating chamber having a heat exchange duct therein; b. ducts connecting said heat exchange duct across said chamber inlet and outlet to establish a closed pneumatic circuit through said chamber; c. means for driving hot air through said heating chamber over said heat exchange duct; and, d. means for circulating gas through said closed pneumatic circuit while said hot air is being driven through said heating chamber so as to heat said heat-retaining material.
 13. Apparatus for delivering pressurized gas to the intake duct of the air turbine starter of a gas-driven turbine comprising in combination: a. a tank for holding cryogenic liquid; b. a pressure vessel for holding hot gas under pressure and having an inlet for receiving cryogenic liquid from said tank and an outlet for discharging hot gas under pressure to said intake duct; c. means for feeding cryogenic liquid from said tank into said pressure vessel; d. means for vaporizing the cryogenic liquid in said pressure vessel and for raising the resulting gas to a predetermined temperature and pressure; and e. means for opening said outlet while said resulting gas is at said predetermined temperature and pressure.
 14. Apparatus in accordance with claim 13 and further characterized in that: a. said pressure vessel additionally includes a second inlet and a second outlet; and, b. said means for vaporizing includes:
 15. Apparatus in accordance with claim 14 and further characterized by: a. means operable only in the absence of pressure within said pressure vessel for actuating said second inlet and second outlet opening means; b. means for actuating said hot-gas-forcing means in response to the actuation of said second inlet and second outlet opening means; c. means for actuating said second inlet and second outlet closing means in response to said matrix of heat-retaining material reaching a predetermined temperature; and, d. means for deactivating said hot-gas-forcing means in response to said matrix of heat-retaining material reaching said predetermined temperature.
 16. Apparatus in accordance with claim 13 and further characterized by means for increasing the rate of flow of cryogenic liquid into said pressure vessel in response to a drop in the pressure in said pressure vessel below a predetermined level so as to counteract said drop in pressure. 